Which cpt code do you add the 25 modifier to when billing 99283 and 99213?

The 25 modifier is typically added to the evaluation and management (E/M) service code that is billed separately when a procedure or service is performed on the same day. In this case, if both 99283 (Emergency department visit, low to moderate severity) and 99213 (Office or other outpatient visit, established patient) are billed, the 25 modifier is generally added to the code that represents the more comprehensive service. If both codes are necessary, ensure that the documentation supports the medical necessity for each service.